In the case of luminescence diode chips which are electrically contact-connected using a bonding wire, a comparatively small central region of the chip surface is generally provided with a contact area (bonding pad) in order to connect the bonding wire. Since luminescence diode chips are generally mounted on a carrier or in an LED housing with a chip surface that is opposite the bonding wire, the chip surface on which the bonding pad is arranged is the radiation exit area, that is to say the chip surface from which at least the predominant part of the electromagnetic radiation generated in an active zone of the luminescence diode chip is coupled out of the luminescence diode chip.
In the case of conventional luminescence diode chips which have an edge length of less than 300 μm, a comparatively homogeneous current distribution can be achieved in the luminescence diode chip using a bonding pad which is centrally arranged on the radiation coupling-out area. However, in the case of large-area luminescence diode chips having an edge length of up to 1 mm, for example, this type of contact-connection may disadvantageously result in inhomogeneous current feed to the luminescence diode chip which results in an increased forward voltage and in low quantum efficiency in the active zone. This effect occurs, in particular, in semiconductor materials having a low transverse conductivity, for example in nitride compound semiconductors. In this case, the maximum current density occurs in a central region of the luminescence diode chip and decreases, starting from the central bonding pad, in the direction of the side flanks as the distance from the bonding pad increases. This results in an often undesirable non-uniform brightness of the radiation exit area. Furthermore, it is disadvantageous that the radiation emitted in the central region of the luminescence diode chip, in which the greatest current density occurs, is at least partially emitted toward the non-transparent bonding pad and is thus at least partially absorbed.
De 199 47 030 A1 discloses the practice of providing the radiation coupling-out area of an InGaAlP LED with a contact structure, which comprises a central bonding pad and a plurality of contact webs which are connected to the bonding pad, in order to achieve better current expansion.